1. Field of the Invention
The present invention relates generally to engagement systems for use in an automotive vehicle, and more particularly relates to an electro mechanical engagement system for use in combination with a friction clutch to control the torque in the driveline of a vehicle.
2. Description of Related Art
Torque distribution systems in automotive vehicles have been known for many years. The torque distribution systems are used on either a front axle or a rear axle or between the axles of an automotive vehicle. Generally, the torque distribution systems deliver torque to a wheel at all times at a fixed percentage or in an on demand manner. Torque distribution systems have some type of engagement system that will engage a friction clutch which includes a plurality of plates therein. Many types such as electrical, hydraulic and mechanical or electro mechanical systems have been designed for engaging the friction clutch. One of the more popular existing designs is the use of a ball ramp mechanism to convert rotation into axial displacement. This axial displacement is created by taking the torque load from the rotation of the ball ramp mechanism and transforming that torque into an axial force which is applied to a friction clutch. These friction clutches will then distribute torque to the prop shafts or side shaft of a vehicle in a variety of manners by the torque distribution system.
There are numerous different design variations of the prior art ball ramp mechanisms. Generally, the ramp angle of the ball ramp mechanism defines the ratio of the torque vs. force conversion as well as the necessary rotation angle needed to achieve the required axial travel. In these prior art systems the required axial travel to engage the clutch pack is defined by the sum of the build tolerances, clutch pack settling and wear, and the required clutch pack clearance in its open condition. Furthermore, these prior art systems have a required number of balls within the ball ramp mechanism and a predetermined circumference of the ball circle which also defines the available rotational angle, which then in combination with any ramp angles of the ball ramp mechanism defines the available axial stroke.
However, the prior art ball ramp mechanisms do have a number of drawbacks. One such drawback is that in order to limit the required engagement torque a small ramp angle is required, however, at the same time to provide maximum engagement travel, with the maximum number of balls, a steep ramp angle is necessary. These two requirements are contrary to each other and lead to a compromised design in all of the prior art ball ramp mechanisms in terms of shimming the clutch pack to minimize the tolerances and using high engagement torques necessary for the required engagement travel. Another problem with the prior art devices is that the required axial force necessary to operate the ball ramp mechanism during engagement is not constant, it tends to be small or low while the ball ramp mechanism system removes any clearances such as tolerances, clutch pack clearance to reduce losses. The force then increases in a progressive manner when the clutch pack actually begins its engagement. A constant ramp angle would not encounter this variation of axial force during engagement. Other attempts to over come this non-constant axial force during engagement have been tried such as, a ramp with a digressive angle however, this digressive angle ramp will only work if the position of the balls is perfectly defined in relation to the engagement arrangement of the clutch. Furthermore, built in tolerances and clutch pack wear will effect the working position of the balls during engagement and therefore the function of the digressive ramp. This causes problems with engagement and the amount of time required to engage the clutch pack as necessary.
Therefore, there is a need in the art for a ball ramp mechanism that applies a constant axial force during engagement of the clutch pack while also reducing the lag time for actual clutch engagement to occur. Furthermore, there is a need in the art for a more precise control of the amount of axial load being placed against the clutch pack thus ensuring a more definitive response rate to on road vehicle conditions.
One object of the present invention is to provide an improved electro mechanical engagement system for a friction clutch.
Another object of the present invention is to provide a double stage ramp mechanism for an electro mechanical engagement system.
Yet a further object of the present invention is to provide an engagement mechanism that automatically switches from a high ramp angle to a small ramp angle during the different stages of a clutch pack engagement.
A further object of the present invention is to provide an engagement mechanism that minimizes the required angular rotation and torque necessary by maximizing the engagement force and the engagement stroke.
To achieve the fore going objects an engagement mechanism for use in a housing in an automotive vehicle is disclosed. The engagement mechanism includes a first ball ramp disc engaging the housing on one side. The engagement mechanism further includes a second ball ramp disc adjacent to the first ball ramp disc on the side opposite the housing. The engagement mechanism also includes a spring arranged between the first ball ramp disc and the second ball ramp disc. The first ramp disc includes a first ramp on the side engaging the housing and a second ramp on the side opposite of the first ramp. The second ball ramp disc includes a ramp on the side adjacent to the first ball ramp disc.
One advantage of the present invention is a new and improved electro mechanical engagement system for a friction clutch.
Another advantage of the present invention is a double stage ramp mechanism for use in a friction clutch.
A further advantage of the present invention is an engagement mechanism that has a self-adjusting mechanism.
Yet another advantage of the present invention is an engagement mechanism that provides a low angle engagement ratio at low engagement forces and a high ratio once the clutch requires high engagement forces.
Yet a further advantage of the present invention is that the engagement mechanism minimizes the required angular rotation and torque necessary by maximizing the engagement force and the engagement stroke.
Still another advantage of the present invention is that the mechanism switches automatically from a high ramp angle to a small ramp angle depending on the different stages of the clutch pack engagement.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.